The present invention relates to a semiconductor memory.
A conventional semiconductor memory does not include a write means for simultaneously writing data in a plurality of memory cells during a test, and a means for comparing expected value data input during a test and data read out from the plurality of memory cells. Therefore, in the test of the semiconductor memory of this type, data read/write access is performed for each memory cell in a memory cell array, and comparison for detecting a coincidence between readout data and expected value data is performed by a memory tester. For the purpose of shortening a test time, identical test data is written in memory cells corresponding to four bits in a memory cell array. Then, an AND result of the data read out from these memory cells is sent to the memory tester so as to perform coincidence detection of all the readout data and comparison associated with coincidence detection with expected value data. This technique is described in 1985 IEEE, International Solid State Circuits Conference, pp. 240-241, A 90 ns 1M bit DRAM with multi bit test mode, KUMANOYA.
In a conventional semiconductor memory, the test is performed by a comparison operation for each memory cell. Therefore, along with an increase in memory capacity of the semiconductor memory, a test time is considerably prolonged. For example, when a test is conducted in 300-ns cycles using "MSCAN" as one of a simplest test data or "CHECKERBOARD" suitable for detecting interference between adjacent memory cells, a semiconductor memory having a memory capacity of 256 kb (kilobits) requires only a test time of 0.3 sec for each test data. In a similar test by an operation for simultaneously comparing several bits, the test time only takes 0.1 sec or less for each test data.
However, if the memory capacity is increased up to 16 Mb (megabits), the test times for the above test data are respectively prolonged to 20 sec and 5 sec. An increase in test time causes an increase in cost of the semiconductor memory, and disturbs mass production.